1. Field of the Invention
The present invention relates to a system for coating weld joints in a pipeline. More particularly, the present invention relates to an assembly and process for heating a weld joint and thereafter applying a coating to the heated weld joint.
2. Prior Art
Various methods and systems are used to cover the weld joints of a pipeline which has been made up from pipe sections welded together in end-to-end relation. These pipe sections have been previously coated at the mill, except for the ends, which as indicated above, are welded together in the field. The pipe joints are then protected from corrosion by coating them in the field with an epoxy material, or with a polyethylene material, or by covering these weld joints with asphalt sleeves or heat-shrinkable polyethylene sleeves.
In Hart U.S. Pat. No. 4,308,819, issued on Jan. 5, 1982 and entitled "System for Spraying Fludized Powder Circumferentially Around a Pipe Joint" there is disclosed a powder applicator ring which is comprised of three arcuate frame members which connect together by a latching means to circumferentially engage a pipe around a weld joint. The ring is capable of moving circumferentially around the pipe by means of belts which engage the surface of the pipe. Powder dispensers are mounted on the ring and are adapted to spray powder onto the weld joint which has been previously heated by a separate apparatus.
In Betteridge et al U.S. Pat. No. 4,595,607, issued on June 17, 1986 and entitled "Combined Induction Heating and Coating System for Pipe Weld Joints" there is disclosed a ring which is divided into three arcuate sections that encircle the pipe and which are adapted to move circumferentially around the weld joint by means of a plurality of belts or wheels which engage the surface of the pipe. In the Betteridge et al patent, the powder dispensers are also mounted on the ring as in the case of the Hart patent referred to above. However, the Betteridge et al patent has a plurality of induction heaters mounted in the ring for heating the weld joint prior to the application of the powdered material.
In Hart et al U.S. patent application Ser. No. 07/415,518 filed Oct. 2, 1989, assigned to the owner of the present invention, and entitled "Sleeve Applicator Assembly for Pipe Joints", there is shown a stationary frame which is attached to a pipe adjacent a weld joint. A ring composed of two arcuate elements which can be connected together to form a closure is positioned adjacent the frame for rotation around the weld joint. Drive means mounted on the stationary frame engages the ring to rotate the latter around the weld joint. The aforementioned ring of the Hart et al application is designed to apply a sheet of shrinkable material to the weld joint. The ring also includes a pair of spaced induction heating means which are similar to the heating means to be disclosed in the present invention.